Electrical ceiling heating in tunnel kilns

ABSTRACT

An electrical heating device in a tunnel kiln comprises a plurality of U- or double U- shaped heating elements disposed transversely across the top of the tunnel. The elements are only supported at each end by pipe like members of aluminiferous material about which the bends of the elements are looped. The pipe like elements are inclined inwardly towards the center of the tunnel at an angle of 10* to the vertical.

United States Patent 1 Petzi et al. July 3, 1973 ELECTRICAL CEILING HEATING IN 1.864.334 6/1932 Baily l3/25 U E KI 2,264,716 12/1941 Roth 13/25 [76] Inventors: Fritz Petzi, Michelfelder Str. 9;

Helmut Baumann, Fuchtbauer Str. 5, P i r Ex iner- Ro N. Envall, Jr. both of 8500 Numbel'gi Germany An0rneyKenwood Ross et al. [22] Filed: Dec. 27, 1971 [21] App]. No.: 212,406

[57] ABSTRACT [30] Foreign Application Priority Data An electrical heating device in a tunnel kiln comprises NOV. 10, 1971 Germany P 21 55 a plurality of U- or U- haped heating elements disposed transversely across the top of the tunnel. The US. Cl. elements are only upported at each end III". Cl. members of aluminiferous material about the Fleld of Search bends of the elements are looped The elements are inclined inwardly towards the center of the References Cited tunnel at an angle of 10 to the vertical.

UNITED STATES PATENTS 1,547,000 7/1925 Ruckstuhl 13/25 4 Claims, 3 Drawing Figures ELECTRICAL CEILING HEATING IN TUNNEL KILNS The invention relates to electrical ceiling heating in tunnel kilns for the ceramic industry by means of heating elements bent in U-shaped configuration, more especially in double U-shaped configuration, which extend transversely to the longitudinal walls of the kiln.

The heating elements used for producing high temperatures are formed from bare unprotected heat conductors which have only slight strength and tend to break easily. On account of these characteristics it is customary to arrange ceramic supporting plates under the heating elements in the ceiling of the kiln and to rest the heating elements loosely on these supporting plates. It is also customary not to place the heating conductors directly onto the ceramic plates, but onto loose grains of highly aluminiferous material, which grains are expressly placed on the ceramic plates so that the heating conductors can contract and expand due to thermal effects in a substantially unhindered manner.

A disadvantage in the known type of design of the electrical tunnel kiln ceiling heating, is that, for heating the material to be fired, by way of example for sintering electrical and magnetic materials, the heat conductors have to provide, from above, not only the useful heat for the firing of the material, but also the heat which is required to overcome the thermal insulation of the supporting plates. Apart from the necessity of having to supply the heat loss caused by the supporting plates, the supporting plates cause in addition a temporal delay of the heat conduction and require, moreover, a higher temperature of the heating conductor than would be necessary if the heat could be directed directly from the heating conductor to the goods for firing. Preventing direct heating of the article to be fired from above, however, at least in the high temperature ranges, is the fact that here the intrinsic weight of the heating conductors is already likely to bring about too great a sagging of the conductors leading to destruction thereof.

The problem underlying the invention is to preclude in the case of electrical ceiling heating in tunnel kilns for the ceramic industry by means of heating elements bent in U-shaped configuration, more especially in double U-shaped configuration which extend transversely to the longitudinal walls of the kiln, the disadvantages which have hitherto been caused by the supporting plates which bear the heating elements. The problem thereby posed is solved, in the case of an electrical ceiling heating of the said kind, in accordance with the invention, in that provided in the region of the bends of the heating elements on the side walls of the kiln, or on kiln bricks projecting towards the inner space of the kiln, there is respectively at least one upwardly projecting finger made of highly aluminiferous material, and in that the bends of the heating elements loop around the fingers to be retained thereby and, moreover, span the kiln space free of support.

It is advantageous if the free ends of the fingers are inclined slightly towards the inner space of the kiln, by way of example have an angle of in relation to the perpendicular side walls of the kiln. Moreover, it is adviseable for the length of the freely upwardly projecting finger part to amount to at leastone-fifth of the clear width of the kiln channel.

Tests have shown that, with use of the invention, the heating conductors withstood, even in the case of fairly long use of the kiln, the thermal and mechanical stresses despite their slight inherent strength, contrary to what was to be expected. Of course, what is important is that the fingers consist of a highly aluminiferous material which does not react chemically with the heating conductor, which softens on the upper surface at a high temperature, and more especially is not adhered thereto, so that the heat conductors remain movable at the points of suspension.

It is in addition favorable if the fingers are inserted with their lower ends securely held in a kiln brick. Moreover, it is advisable for the fingers to be shaped similarly to short pipe-pieces and for the kiln bricks receiving the fingers to be rounded downwards towards the kiln space from the front upper side. Due to this rounding the effect is that the heating conductors can carry out their own motions largely without resistance, more especially as they are not exposed to any mechanical attacks by points or edges.

The insertion of the highly aluminiferous fingers into the kiln bricks leads, above all, to a considerable saving in costs in the production of the heating element mounting support.

The mounting, in accordance with the invention, of the electrical heating elements on the ceiling of the tunnel kiln produces, in addition to abolishing the disadvantages caused by the previous use of supporting plates, in addition the further advantages that the heating elements can be exchanged individually without having to interrupt the operation of the kiln. To exchange the elements it is sufficient to remove from the outside the stopper bricks at the heating element in question and to exchange this latter for a new heating element and to replace the stopper bricks.

Further advantages and features are explained in the following description of the drawings which illustrate one exemplified embodiment and in which:

FIG. 1 is a diagrammatic representation of an electrically heated sliding plate tunnel kiln, in longitudinal section;

FIG. 2 is a partial section, illustrating the side view of an installed heating conductor, through the tunnel kiln in accordance with FIG. 1;

FIG. 3 is a section along the line III-III in FIG. 2.

A tunnel kiln has, in known manner along its channel 1, a pre-heating zone A, a firing zone B and a cooling zone C. Serving for the transportation of the articles to be fired from entrance end 2 to exit end 3' are sliding plates 4 which are moved along the channel 1, and thus conduct the article to be fired W (FIG. 2) which is carried by the plates 4, through the zones A, B and C.

Serving to heating the article W from above for firing is an electrical ceiling heating which is formed from bare metal heating conductors 5 which are bent in double U-shaped configuration and which loop around, with their bends 6, 7 and 8, fingers 9, 10 and 11. In this way, they span the kiln channel 1 suspended in the air, so that the heat they produce arrives, without any hinderance, from above directly on the article W to the fired. The fingers 9, l0 and 11 are designed in the shape of round tubes and consist of a highly aluminiferous material which does not react chemically with the material, of the heating elements 5, which softens at a high heating temperature on its upper surface. At the high temperature the heating conductor does as expected expand and sag towards the center of the channel 1, as is indicated by the dot-dash double line 5 in FIG. 2, but the suspension of the heating conductors from the fingers along the heating section is maintained in such a way that, even in the case of a maximum sagging D, no contact takes place between the heating conductor and the article being fired.

The fingers 9, 10, 11 are inserted into the kiln bricks 13, 14, 15. Their free ends are slightly inclined towards the inner space 1 of the kiln by the angle a; they form, by way of example in relation to the perpendicular sidewalls 16, 17 of the kiln, an angle A of It has additionally proved to be favorable to dimension the length L of the freely upwardly projecting part of the fingers at least one-fifth as great as the clear width B of the kiln channel 1. The kiln bricks l3, l4, 15, into which the lower parts of the fingers are inserted for support overhang with their front ends 18 the kiln channel to a certain extent. They have, furthermore, on their upper side, facets 19 which are inclined by way of example by in relation to the horizontal plane. The facets 19 virtually preclude the heating conductors from being damaged if they expand or contract.

If, for any reason, a heating element has to be exchanged during the operation of the tunnel kiln, then it is sufficient to remove a lateral stopper brick 20, whereupon it is readily possible to remove the heating element in question out of the kiln through the access thus provided and, if necessary, to replace it by a new heating element, without having to interrupt the operation of the kiln. Because of the inclination of the fingers by an angle a, the exchange can be effected easily, even after sagging of the heating conductors has taken place, because, upon applying a comparatively slight pull, the bending points 6, 7, 8 readily slide over the fingers 9, 10, 11.

I claim:

1. An electrical ceiling heating means in a tunnel kiln for the ceramic industry comprising: heating elements bent in U-shaped configuration and extending transversely between the longitudinal walls of the kiln across the tunnel, the regions of the bending points of the heating elements being supported relative to the longitudinal walls of the kiln, upwardly projecting fingers made of a highly aluminiferous material and supported by the longitudinal, walls of the kiln, the heating elements with their bends being looped around the fingers and spanning the kiln space free from other support, the free ends of the fingers being slightly upwardly inclined towards the inner space of the kiln at a 10 angle.

2. An electrical ceiling heating means as claimed in claim 1, characterized in that the length of the freely upwardly projecting part of a finger equals at least onefifth of the inner width of the kiln channel.

3. An electrical ceiling heatingmeans as claimed in claim 1, the fingers being shaped as round tubes.

4. An electrical ceiling heating means as claimed in claim 1, characterized in that the kiln bricks receiving the fingers each have a facet inclined downwardly from the upper kiln side towards the kiln space. 

1. An electrical ceiling heating means in a tunnel kiln for the ceramic industry comprising: heating elements bent in U-shaped configuration and extending transversely between the longitudinal walls of the kiln across the tunnel, the regions of the bending points of the heating elements being supported relative to the longitudinal walls of the kiln, upwardly projecting fingers made of a highly aluminiferous material and supported by the longitudinal walls of the kiln, the heating elements with their bends being looped around the fingers and spanning the kiln space free from other support, the free ends of the fingers being slightly upwardly inclined towards the inner space of the kiln at a 10* angle.
 2. An electrical ceiling heating means as claimed in claim 1, characterized in that the length of the freely upwardly projecting part of a finger equals at least one-fifth of the inner width of the kiln channel.
 3. An electrical ceiling heating means as claimed in claim 1, the fingers being shaped as round tubes.
 4. An electrical ceiling heating means as claimed in claim 1, characterized in that the kiln bricks receiving the fingers each have a facet inclined downwardly from the upper kiln side towards the kiln space. 